How common is bipolar II disorder, and are we frequently missing the diagnosis?

The answer depends on who you talk to. On the one hand we have the extreme viewpoint of Akiskal and colleagues, who argue that half of all patients presenting with depression actually have bipolar II disorder and that if you dig deep enough, you will find not one or two varieties of bipolar disorder, but six! These include such species as bipolar I ½ (depression with protracted hypomania), bipolar II ½ (cyclothymic depression), and bipolar IV (hyperthymic depression) (Psychiatr Clin North Am 1999;22(3):517-34).

On the other side of the spectrum, we have stodgy old DSM-IV, which maintains that there are only two bipolars – I and II – and that the prevalence rate of bipolar II is only 1.6%. An excellent review of bipolar II disorder (Can J Psychiatry 2004;49:802-812) synthesizes recent epidemiological data and concludes that the true prevalence may be closer to 5% or 6%.

For us clinicians, the most crucial issue concerning bipolar II, regardless of its prevalence, is whether the diagnosis adds anything helpful to our treatment decisions. Since bipolar II patients almost always present to psychiatrists with depression, they are often mistakenly diagnosed with recurrent major depressive disorder. But does this “mistake” have negative treatment implications?

The few clinical trials conducted specifically with bipolar II patients imply that the answer is no. According to these studies, when you give depressed bipolar II patients SSRIs or SNRIs without mood stabilizers, they respond well, and switch rates to hypomania were quite low, in the range of 3%-8% (J Clin Psychopharmacol 1998;18:435-440; Bipolar Disord 2004;6:75-81).

What about those rare bipolar II patients who present to you with hypomania – surely, these patients should be treated differently from unipolar depressed patients. While most clinicians would say that hypomania responds to the same medications as mania (mood stabilizers and antipsychotics), a Medline search revealed no controlled clinical trials of medications specifically for the treatment of hypomania.

In the latest category bender, one group of researchers published a small study indicating that antidepressants actually act as mood stabilizers in patients with bipolar II (J Affect Disord 2006;92:205-14). In this pilot study, 10 patients with bipolar II were randomized to Lexapro (escitalopram) 10 mg/day vs. placebo for three months of treatment, and then each group crossed over to the other treatment arm for the next three months. The results? Lexapro was better than placebo in terms of improving depression and reducing the percentage of days in either depression or hypomania.

If these results are replicated in larger samples, we’ll have an even harder time arguing that distinguishing between bipolar II and depression is useful.

TCPR Verdict:
Is it Bipolar II? Or simply depression "plus?"